In general, an insulator dash 2 is installed at the interior side surface of a dash panel 1 which separates an engine room E and a cabin R from each other, as shown in FIG. 24. The insulator dash 2 comprises a sound shielding layer 3 made of a material with a high density, such as a recycled rubber sheet, a recycled polyvinylchloride sheet, or the like, and a sound absorbing layer 4 formed of a fiber assembly, which is provided at the back side of the sound shielding layer and is integrally laminated to the sound shielding layer, as shown in the enlarged view of FIG. 25. A floor carpet 5 is laid over the surface at the lower side of the insulator dash 2 in a lapping manner. Also, the upper portion of the insulator dash 2 is positioned inside an instrument panel 6.
The soundproofing mechanism of the conventional insulator dash 2 having a two-layer structure will be described with reference to FIG. 26. A part of noise f1 from an engine or the like and auxiliary equipment provided in the engine room E is shielded by the dash panel 1, and the remaining noise is transmitted through the dash panel 1 and propagates to the cabin side. Noise represented by f2 enters the insulator dash 2.
Then, a part of the noise f2 is absorbed by the sound absorbing layer 4, and is shielded by the sound shielding layer 3. However, a part thereof, represented by f3, enters the instrument panel 6.
Moreover, the transmission noise f3, which has entered the instrument panel 6, is reflected from the inner surface of the instrument panel 6. The reflected noise f4 is reflected from the sound shielding layer 3 again. As a result, the reflected noise f4 and f5 become echoes in the space formed by the instrument panel 6. These echoes significantly prevent a silentness in the cabin.
According to this conventional soundproofing (sound-shielding and sound absorption) mechanism, the ratio of the sound shielding and absorption by the insulator dash 2 to the sound absorption in the instrument panel 6 is about 9:1.
As described above, the conventional insulator dash 2 is composed of a two-layer laminate assembly which comprises the sound shielding layer 3 made of a high density material and the sound absorbing layer 4 made of a fiber assembly. In this case, in particular, the weight of the sound shielding layer 3 increases and this goes against the lightening of products in weight, and deteriorates the efficiency of the fuel consumption and decreases the efficiency of installing operation of the insulator dash 2.
Moreover, according to the soundproofing mechanism of the conventional insulator dash 2, the efficiency of the sound absorption of the instrument panel 6 is very low compared with the efficiency of the sound shielding and absorption of the insulator dash 2, which is mainly due to the double wall sound shielding function. Thus, for soundproofing, elimination of the transmission sound, which previously could not be attenuated in the instrument panel 6, has been a problem to be urgently solved.
The present invention has been devised in view of the foregoing, it is an object of the present invention to provide a sound insulator to be installed at the interior side surface of a body panel, wherein the soundproofing material is lightened by abolishing a sound shielding layer with a large weight and has an increased soundproofing property, and a method for manufacturing the same.